Semiconductor light emitting device and method for manufacturing same

ABSTRACT

A semiconductor light emitting device according to an embodiment includes a stacked body. The stacked body includes a first semiconductor layer of a first conductivity type, a light emitting layer is provided on the first semiconductor layer, and a second semiconductor layer of a second conductivity type provided on the light emitting layer. The stacked body includes a first protrusion on an upper surface of the stacked body. The first protrusion protrudes in a first direction from the first semiconductor layer to the light emitting layer. Length of the first protrusion in a second direction perpendicular to the first direction decreases toward the first direction. The first protrusion includes a first portion and a second portion. The first portion has a first side surface inclined with respect to the first direction. The second portion is provided below the first portion and having a second side surface inclined with respect to the first direction. The second side surface is curved so as to be convex downward.

TECHNICAL FIELD

Embodiments of the invention relate to a semiconductor light emittingdevice and a method for manufacturing the same.

BACKGROUND ART

A semiconductor light emitting device includes a p-type semiconductorlayer, a light emitting layer, and an n-type semiconductor layer. Byapplication of voltage to the semiconductor light emitting device andinjection of carriers into the light emitting layer, light is emittedfrom the light emitting layer. It is desired that the light emitted fromthe light emitting layer be efficiently extracted to the outside of thesemiconductor light emitting device.

CITATION LIST Patent Literature

[Patent Citation 1] JP 2008-60331 A

SUMMARY Technical Problem

A problem to be solved by the invention is to provide a semiconductorlight emitting device and a method for manufacturing the same capable ofimproving the light extraction efficiency.

Solution to Problem

A semiconductor light emitting device according to an embodimentincludes a stacked body. The stacked body includes a first semiconductorlayer of a first conductivity type, a light emitting layer is providedon the first semiconductor layer, and a second semiconductor layer of asecond conductivity type provided on the light emitting layer. Thestacked body includes a first protrusion on an upper surface of thestacked body. The first protrusion protrudes in a first direction fromthe first semiconductor layer to the light emitting layer. Length of thefirst protrusion in a second direction perpendicular to the firstdirection decreases toward the first direction. The first protrusionincludes a first portion and a second portion. The first portion has afirst side surface inclined with respect to the first direction. Thesecond portion is provided below the first portion and having a secondside surface inclined with respect to the first direction. The secondside surface is curved so as to be convex downward.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view showing a semiconductor light emitting device1 according to a first embodiment.

FIG. 2 is an enlarged plan view showing part of the upper surface of thesemiconductor light emitting device according to the first embodiment.

FIG. 3 is a sectional view taken along A-A′ in FIG. 2.

FIGS. 4A to 4C are process sectional views showing the process formanufacturing the semiconductor light emitting device according to thefirst embodiment.

FIGS. 5A to 5C are process sectional views showing the process formanufacturing the semiconductor light emitting device according to thefirst embodiment.

FIGS. 6A and 6B are process sectional views showing the process formanufacturing the semiconductor light emitting device according to thefirst embodiment.

FIG. 7A to 7C are enlarged process sectional views showing the processfor manufacturing the semiconductor light emitting device according tothe first embodiment.

FIG. 8 is an enlarged plan view showing part of the upper surface of asemiconductor light emitting device according to a first variation ofthe first embodiment.

FIG. 9 is a sectional view taken along A-A′ in FIG. 8.

FIG. 10 is an enlarged plan view showing part of the upper surface of asemiconductor light emitting device according to a second variation ofthe first embodiment.

FIG. 11 is a sectional view taken along A-A′ in FIG. 10.

FIG. 12 is an enlarged plan view showing part of the upper surface of asemiconductor light emitting device according to a third variation ofthe first embodiment.

FIG. 13 is a sectional view taken along A-A′ in FIG. 12.

FIG. 14 is an enlarged sectional view showing part of the upper surfaceof a semiconductor light emitting device according to a third variationof the first embodiment.

FIG. 15 is an enlarged plan view showing part of the upper surface of asemiconductor light emitting device according to a fifth variation ofthe first embodiment.

FIG. 16 is a sectional view taken along A-A′ in FIG. 15.

FIG. 17 is a sectional view of a semiconductor light emitting deviceaccording to a second embodiment.

FIG. 18 is an enlarged sectional view showing part of the upper surfaceof the semiconductor light emitting device according to the secondembodiment.

FIG. 19 is a sectional view of a semiconductor light emitting deviceaccording to a first variation of the second embodiment.

FIG. 20 is an enlarged sectional view showing part of the upper surfaceof the semiconductor light emitting device according to the firstvariation of the second embodiment.

FIG. 21 is a sectional view of a semiconductor light emitting deviceaccording to a second variation of the second embodiment.

FIG. 22 is a partially enlarged plan view of the stacked body LB of thesemiconductor light emitting device according to the second variation ofthe second embodiment.

FIG. 23 is a sectional view taken along A-A′ in FIG. 22.

DETAILED DESCRIPTION

Embodiments of the invention will now be described with reference to thedrawings.

The drawings are schematic or conceptual. The relationship between thethickness and the width of portions, the proportion of size betweenportions, etc., are not necessarily the same as the actual valuesthereof. The dimension and/or the proportion may be illustrateddifferently between the drawings, even in the case where the sameportion is illustrated.

In the description and the drawings, the same elements as alreadydescribed are marked with the same numerals, and a detailed descriptionthereof is omitted as appropriate.

An XYZ orthogonal coordinate system is used in describing theembodiments. The direction from the p-type semiconductor layer 109 tothe light emitting layer 111 is referred to as Z-direction (firstdirection). The directions perpendicular to the Z-direction andorthogonal to each other are referred to as X-direction (seconddirection) and Y-direction.

First Embodiment

FIG. 1 is a sectional view showing a semiconductor light emitting device1 according to a first embodiment.

The semiconductor light emitting device 1 is e.g. a light emitting diodeof the vertical conduction type.

As shown in FIG. 1, the semiconductor light emitting device 1 includes asubstrate 101, a p-side electrode 103, a metal layer 105, a contactlayer 107, a stacked body LB, an n-side electrode 115, and an insulatinglayer 117. The stacked body LB includes a p-type semiconductor layer109, a light emitting layer 111, and an n-type semiconductor layer 113.

The substrate 101 is e.g. a silicon substrate. The substrate 101 has anupper surface US and a lower surface BS opposed to each other.

The p-side electrode 103 is provided on the lower surface BS of thesubstrate 101. The p-side electrode 103 contains e.g. metal such asgold, nickel, titanium, and aluminum.

The metal layer 105 is provided on the upper surface US of the substrate101. The metal layer 105 contains e.g. tin.

The contact layer 107 is provided on the metal layer 105. The contactlayer 107 is further surrounded with the metal layer 105 along the X-Yplane. The contact layer 107 has a structure in which e.g. a nickellayer and a silver layer are stacked.

The p-type semiconductor layer 109 is provided on the metal layer 105and the contact layer 107. The p-type semiconductor layer 109 is inohmic contact with the contact layer 107. The p-type semiconductor layer109 is e.g. a gallium nitride layer containing p-type impurity. Thep-type impurity can be e.g. magnesium.

The light emitting layer 111 is provided on the p-type semiconductorlayer 109. The light emitting layer 111 is e.g. an undoped galliumnitride layer. Here, “undoped” means that there is no intentional dopingwith impurity.

The n-type semiconductor layer 113 is provided on the light emittinglayer 111. The n-type semiconductor layer 113 is e.g. a gallium nitridelayer containing n-type impurity. The n-type impurity can be e.g.silicon. The upper surface of the stacked body LB (the upper surface ofthe n-type semiconductor layer 113) is roughened to form an asperitystructure.

The n-side electrode 115 is provided on part of the n-type semiconductorlayer 113. The n-side electrode 115 is in ohmic contact with the n-typesemiconductor layer 113. The n-side electrode 115 contains metal such asplatinum, gold, nickel, titanium, and aluminum.

The insulating layer 117 is provided around the stacked body LB alongthe X-Y plane and covers the upper surface of the metal layer 105. Theroughened upper surface of the stacked body LB and the n-side electrode115 are not covered with the insulating layer 117 but exposed.

In operation of the semiconductor light emitting device 1, holes areinjected from the p-type semiconductor layer 109 into the light emittinglayer 111, and electrons are injected from the n-type semiconductorlayer 113 into the light emitting layer 111. Holes and electrons arerecombined in the light emitting layer 111. Thus, light is emitted fromthe light emitting layer 111. The light emitted from the light emittinglayer 111 is extracted outside through the upper surface of the stackedbody LB.

FIG. 2 is an enlarged plan view showing part of the upper surface of thesemiconductor light emitting device 1 according to the first embodiment.

FIG. 3 is a sectional view taken along A-A′ in FIG. 2.

As shown in FIG. 2, a plurality of protrusions 119 are provided on theupper surface of the stacked body LB. In the example shown in FIG. 2,six protrusions 119 are arranged around one protrusion 119. However, thearrangement of the plurality of protrusions 119 is arbitrary.

As shown in FIG. 3, the protrusion 119 has a first portion 119 a and asecond portion 119 b. The first portion 119 a is located in the upperpart of the protrusion 119. The second portion 119 b is provided belowthe first portion 119 a and located in the lower part of the protrusion119.

The upper surface of the protrusion 119 is perpendicular to e.g. theZ-direction. The width (length in the X-direction and the Y-direction)of the protrusion 119 is narrower toward the Z-direction. Thus, the sidesurface S1 of the first portion 119 a and the side surface S2 of thesecond portion 119 b are inclined with respect to the Z-direction. Theside surface S2 is curved so as to be convex downward. The inclinationof at least part of the side surface S2 with respect to the Z-directionis smaller than the inclination of the side surface S1 with respect tothe Z-direction.

In the sectional view shown in FIG. 3, the side surface S1 is parallelto a direction inclined with respect to the Z-direction. However, theside surface S1 may be curved so as to be convex upward.

The first portion 119 a and the second portion 119 b are provided sothat e.g. the length L2 in the Z-direction of the second portion 119 bis longer than the length L1 in the Z-direction of the first portion 119a.

Next, an example of the method for manufacturing the semiconductor lightemitting device 1 according to the first embodiment is described withreference to FIGS. 4A to 7C.

FIGS. 4A to 6B are process sectional views showing the process formanufacturing the semiconductor light emitting device 1 according to thefirst embodiment.

FIG. 7A to 7C are enlarged process sectional views showing the processfor manufacturing the semiconductor light emitting device 1 according tothe first embodiment.

First, a substrate 131 for growing a nitride semiconductor layer isprepared. The substrate 131 is e.g. a silicon substrate, a sapphiresubstrate, or a gallium nitride substrate. An n-type semiconductor layer113, a light emitting layer 111, and a p-type semiconductor layer 109are sequentially epitaxially grown on this substrate 131 (FIG. 4A).

Next, a contact layer 107 is formed on part of the p-type semiconductorlayer 109. Subsequently, a metal layer 105 a is formed on the p-typesemiconductor layer 109 so as to cover the contact layer 107 (FIG. 4B).Subsequently, the n-type semiconductor layer 113, the light emittinglayer 111, the p-type semiconductor layer 109, and the metal layer 105 aare patterned to remove part of each outer periphery (FIG. 4C).

Next, another substrate 101 different from the substrate 131 isprepared. A metal layer 105 b is formed on the substrate 101.Subsequently, the metal layer 105 a provided on the substrate 131 andthe metal layer 105 b provided on the substrate 101 are bonded to eachother (FIG. 5A). The metal layers 105 a and 105 b bonded together formsa metal layer 105 shown in FIG. 1.

Next, the substrate 131 is stripped by irradiation with UV light fromthe substrate 131 side (FIG. 5B). Subsequently, the p-type semiconductorlayer 109, the light emitting layer 111, and the n-type semiconductorlayer 113 are patterned. Thus, a stacked body including the p-typesemiconductor layer 109, the light emitting layer 111, and the n-typesemiconductor layer 113 is formed on each contact layer 107 (FIG. 5C).

Next, an insulating layer 117 covering the p-type semiconductor layer109, the light emitting layer 111, and the n-type semiconductor layer113 is formed (FIG. 6A). Subsequently, part of the insulating layer 117is removed so as to expose part of the upper surface of each n-typesemiconductor layer 113. An n-side electrode 115 is formed on part ofthe exposed upper surface of the n-type semiconductor layer 113 (FIG.68B).

In the following, the state of part of the upper surface of the n-typesemiconductor layer 113 is described with reference to FIGS. 7A to 7C.

FIGS. 7A to 7C show the state of part of the upper surface of the n-typesemiconductor layer 113 in enlarged view.

After forming the n-side electrode 115, a resist film is applied ontothe n-type semiconductor layer 113. This resist film is patterned byphotolithography to form a resist mask M (FIG. 7A).

Next, the resist mask M is used to etch the n-type semiconductor layer113 by the RIE (reactive ion etching) method. At this time, the n-typesemiconductor layer 113 is etched, and the resist mask M is also etched.The etching rate for the corner part of the resist mask M is higher thanthe etching rate for the upper surface and the side surface of theresist mask M. Thus, the width of the upper part of the resist mask M isgradually narrowed (FIG. 7B). Further continuing etching in this statealso narrows the width of the lower part of the resist mask M, andexposes part of the n-type semiconductor layer 113 originally coveredwith the resist mask M. Then, the newly exposed part of the n-typesemiconductor layer 113 is etched (FIG. 7C).

At this time, in the portion of the n-type semiconductor layer 113 whichwas exposed at the time of forming the resist mask M, etching proceedswith the etched surface curved downward. On the other hand, in the newlyexposed part of the n-type semiconductor layer 113, etching proceeds sothat the etched surface is parallel to a direction inclined with respectto the Z-direction. Alternatively, etching proceeds so that the etchedsurface protrudes upward.

It is considered that such etching occurs for the following reason.

The etching process from FIGS. 7A to 7B is performed by e.g. the RIEmethod in which the acceleration voltage is set low. In the RIE method,part of the n-type semiconductor layer 113 is removed to form adepression. At this time, redeposition of the etched material occurs inthe region from the corner of the bottom part of the depression to thelower end of the resist mask M. This redeposited material suppressesetching of the n-type semiconductor layer 113 directly below the resistmask M. Furthermore, the low setting of the acceleration voltage lowersanisotropy of etching and suppresses re-etching of the redepositedmaterial. Thus, the inner wall of the depression is curved so as to beconvex downward.

In the inner wall of this depression, etching proceeds while keeping thecurved shape also in the process from FIGS. 78 to 7C. Thus, the sidesurface S2 shown in FIGS. 2 and 3 is formed.

In the process from FIGS. 7B to 7C, the width of the resist mask Mdecreases. Thus, another part of the n-type semiconductor layer 113 isexposed and etched. At this time, the n-type semiconductor layer 113 isgradually exposed from the outer periphery side of the resist mask M.Thus, the etching amount of the n-type semiconductor layer 113 increasesfrom the center side toward the outer periphery of the resist mask M.The etched surface is inclined downward from the center side toward theouter periphery of the resist mask M. Thus, the side surface S1 shown inFIGS. 2 and 3 is formed.

Accordingly, a protrusion 119 having a first portion 119 a and a secondportion 119 b is formed.

Then, a p-side electrode 103 is formed on the lower surface of thesubstrate 101. Thus, the semiconductor light emitting device 1 shown inFIGS. 1 to 3 is obtained.

Here, the function and effect according to this embodiment aredescribed.

According to this embodiment, the protrusion 119 has a first portion 119a, and a second portion 119 b with the side surface curved so as to beconvex downward. According to such a configuration, the surface area ofthe upper surface of the stacked body LB can be made larger than in thecase where the side surface of the protrusion 119 is uniformly inclined.

The light emitted from the light emitting layer 111 repeats irregularreflection in each semiconductor layer. This generates light beamstraveling in various directions in the semiconductor light emittingdevice. Thus, the amount of light incident on the interface between theupper surface of the stacked body LB and the outside from inside thestacked body LB does not significantly depend on the inclination of eachportion of the interface with respect to the Z-direction. Furthermore,the amount of external light extraction per unit area at the interfacedoes not significantly depend on the inclination of the interface. Thus,the amount of light extracted outside from the stacked body LB can beincreased by increasing the surface area of the upper surface of thestacked body LB. This can improve the efficiency of light extractionfrom the semiconductor light emitting device.

Here, the side surface S2 of the second portion 119 b is curved so as tobe convex downward. This can reduce the possibility that the lightextracted outside from the n-type semiconductor layer 113 through theside surface S2 is incident on the side surface of the adjacentprotrusion 119 compared with the case where the side surface S2 iscurved so as to be convex upward. The efficiency of light extractionfrom the semiconductor light emitting device can be improved by reducingthe possibility that the extracted light is incident on the side surfaceof the adjacent protrusion 119.

The side surface of the second portion 119 b provided below the firstportion 119 a (in the lower part of the protrusion 119) is curved. Thus,the surface area of the side surface of the protrusion 119 can be madelarger than in the case where the side surface of the first portion 119a is curved.

Furthermore, the length L2 in the Z-direction of the second portion 119b is made longer than the length L1 in the Z-direction of the firstportion 119 a. This can further increase the surface area of the sidesurface of the protrusion 119.

(First Variation)

FIG. 8 is an enlarged plan view showing part of the upper surface of asemiconductor light emitting device 1 a according to a first variationof the first embodiment.

FIG. 9 is a sectional view taken along A-A′ in FIG. 8.

As shown in FIG. 8, in the semiconductor light emitting device 1 a, aplurality of protrusions 119 and a plurality of protrusions 121 areprovided on the upper surface of the stacked body LB. The plurality ofprotrusions 119 and the plurality of protrusions 121 are arranged sothat at least one protrusion 119 is adjacent to one protrusion 121.

As shown in FIG. 9, as in the semiconductor light emitting device 1, theprotrusion 119 has a first portion 119 a and a second portion 119 b. Theprotrusion 121 has a third portion 121 c and a fourth portion 121 d. Thethird portion 121 c is located in the upper part of the protrusion 121.The fourth portion 121 d is provided below the third portion 121 c andlocated in the lower part of the protrusion 121.

The upper surface of the protrusion 121 is perpendicular to e.g. theZ-direction. The width (length in the X-direction and the Y-direction)of the protrusion 121 is narrower toward the Z-direction. Thus, the sidesurface S3 of the third portion 121 c and the side surface S4 of thefourth portion 121 d are inclined with respect to the Z-direction. Theside surface S4 is curved so as to be convex downward. Furthermore, theside surface S3 may be curved so as to be convex upward. The inclinationof at least part of the side surface S4 with respect to the Z-directionis smaller than the inclination of the side surface S3 with respect tothe Z-direction.

The height of the protrusion 121 is lower than the height of theprotrusion 119. More specifically, the length L4 in the Z-direction ofthe fourth portion 121 d is generally equal to the length L2 in theZ-direction of the second portion 119 b. On the other hand, the lengthL3 in the Z-direction of the third portion 121 c is shorter than thelength L1 in the Z-direction of the first portion 119 a.

Thus, the protrusion 121 having a lower height than the protrusion 119is provided. This can reduce the possibility that the light extractedfrom the protrusion 119 is incident on the side surface of theprotrusion 121. Thus, the light extraction efficiency of thesemiconductor light emitting device can be improved.

Here, as shown in FIG. 9, the height of the protrusion 121 is lowered sothat the length L4 is longer than the length L3. This can suppress thedecrease of the surface area in the side surface of the protrusion 121.

(Second Variation)

FIG. 10 is an enlarged plan view showing part of the upper surface of asemiconductor light emitting device 1 b according to a second variationof the first embodiment.

FIG. 11 is a sectional view taken along A-A′ in FIG. 10.

In the semiconductor light emitting device 1 b, a plurality ofprotrusions 119 and a plurality of protrusions 121 are provided on theupper surface of the stacked body LB as in the semiconductor lightemitting device 1 a. The plurality of protrusions 119 and the pluralityof protrusions 121 are arranged so that at least one protrusion 119 isadjacent to one protrusion 121. The spacing between the protrusion 119and the protrusion 121 is wider than the spacing between the protrusions119.

As shown in FIG. 11, as in the semiconductor light emitting device 1,the protrusion 119 has a first portion 119 a and a second portion 119 b.The protrusion 121 has a third portion 121 c and a fourth portion 121 d.The third portion 121 c is located in the upper part of the protrusion121. The fourth portion 121 d is provided below the third portion 121 cand located in the lower part of the protrusion 121.

In the protrusion 121, as in the semiconductor light emitting device 1a, the side surface S3 of the third portion 121 c and the side surfaceS4 of the fourth portion 121 d are inclined with respect to theZ-direction. The side surface S4 is curved so as to be convex downward.

Comparing the protrusion 119 with the protrusion 121 at the sameposition in the Z-direction, the width of the protrusion 121 is narrowerthan the width of the protrusion 119. Thus, for instance, the width W1at the lower end of the third portion 121 c (the upper end of the fourthportion 121 d) is narrower than the width W2 at the lower end of thefirst portion 119 a (the upper end of the second portion 119 b).

Thus, the protrusion 121 having a narrower width than the protrusion 119is provided. This can reduce the possibility that the light extractedfrom the protrusion 119 is incident on the side surface of theprotrusion 121 compared with the semiconductor light emitting device 1.Thus, the light extraction efficiency of the semiconductor lightemitting device can be improved.

(Third Variation)

FIG. 12 is an enlarged plan view showing part of the upper surface of asemiconductor light emitting device 1 c according to a third variationof the first embodiment.

FIG. 13 is a sectional view taken along A-A′ in FIG. 12.

As shown in FIG. 12, a plurality of protrusions 119 and a plurality ofprotrusions 121 are provided on the upper surface of the stacked bodyLB. The width of the protrusion 121 is narrower than the width of theprotrusion 119. In the X-Y plane, the spacing between the protrusion 119and the protrusion 121 is wider than the spacing between the protrusions119.

As shown in FIG. 13, the height of the protrusion 121 is lower than theheight of the protrusion 119. More specifically, the length L4 in theZ-direction of the fourth portion 121 d is shorter than the length L2 inthe Z-direction of the second portion 119 b. The length L3 in theZ-direction of the third portion 121 c is shorter than the length L1 inthe Z-direction of the first portion 119 a.

Thus, the protrusion 121 having a lower height and a narrower width thanthe protrusion 119 is provided adjacent to the protrusion 119. This canfurther reduce the possibility that the light extracted from theprotrusion 119 is incident into the stacked body LB from the protrusion121 compared with the first variation and the second variation.

(Fourth Variation)

FIG. 14 is an enlarged sectional view showing part of the upper surfaceof a semiconductor light emitting device id according to a thirdvariation of the first embodiment.

In the semiconductor light emitting device id, the stacked body LBfurther includes a plurality of undoped semiconductor layers 123. Theplurality of semiconductor layers 123 are spaced from each other on then-type semiconductor layer 113. Part of the upper surface of the n-typesemiconductor layer 113 is exposed through the gap between thesemiconductor layers 123. The semiconductor layer 123 is e.g. an undopedgallium nitride layer. The n-type semiconductor layer 113 is connectedto the n-side electrode 115 through the gap between the semiconductorlayers 123.

As shown in FIG. 14, for instance, the first portion 119 a of theprotrusion 119 is composed of part of the semiconductor layer 123. Partof the second portion 119 b is composed of another part of thesemiconductor layer 123 and part of the n-type semiconductor layer 113.

The light absorption coefficient in the undoped semiconductor layer issmaller than the light absorption coefficient in the impurity-dopedsemiconductor layer. In the semiconductor light emitting device 1 d, atleast part of the protrusion 119 is composed of the semiconductor layer123. This can improve the light extraction efficiency compared with thesemiconductor light emitting device 1.

(Fifth Variation)

FIG. 15 is an enlarged plan view showing part of the upper surface of asemiconductor light emitting device 1 e according to a fifth variationof the first embodiment.

FIG. 16 is a sectional view taken along A-A′ in FIG. 15.

In the semiconductor light emitting device 1 e, a plurality of recessesR are formed in the upper surface of the n-type semiconductor layer 113.

As shown in FIG. 15, the recesses R are provided in a plurality in theupper surface of the n-type semiconductor layer 113 along the X-Y plane.As an example, six recesses R are arranged around one recess R.

As shown in FIG. 16, the width of the recess R is narrowed downward. Therecess R has a side surface S5 and a side surface S6 inclined withrespect to the Z-direction. The side surface S5 is curved so as to beconvex upward. The side surface S6 is located below the side surface S5.

In the recess R, the length L5 in the Z-direction of the portion havingthe side surface S5 is longer than the length L6 in the Z-direction ofthe portion having the side surface S6.

In the example shown in FIG. 16, the side surface S6 is uniformlyinclined downward. However, the side surface S6 may be curved so as tobe convex downward.

The light emitted from the light emitting layer 111 is extracted outsidefrom the upper surface of the stacked body LB. The side surface S5 ofthe recess R is curved so as to be convex upward. Thus, the surface areaof the upper surface of the stacked body LB can be made larger than inthe case where the side surface of the recess R is uniformly inclined.That is, this variation can improve the efficiency of light extractionfrom the semiconductor light emitting device as in the semiconductorlight emitting devices 1-1 d.

Here, the length L5 is made longer than the length L6. This can furtherimprove the efficiency of light extraction from the semiconductor lightemitting device.

Also in this variation, as in the semiconductor light emitting deviceid, an undoped semiconductor layer 123 may be provided on the n-typesemiconductor layer 113. The recess R may be formed in the semiconductorlayer 123 and the n-type semiconductor layer 113.

Such a configuration can further improve the efficiency of lightextraction from the semiconductor light emitting device.

Second Embodiment

FIG. 17 is a sectional view of a semiconductor light emitting device 2according to a second embodiment.

The semiconductor light emitting device 2 is e.g. a light emitting diodeof the lateral conduction type.

As shown in FIG. 17, the semiconductor light emitting device 2 includesa substrate 201, an n-side electrode 203, a metal layer 205, a barrierlayer 207, an n-side contact layer 209, an insulating layer 211, abarrier layer 213, a p-side contact layer 215, a p-type semiconductorlayer 217, a light emitting layer 218, a spacer 221, an n-typesemiconductor layer 219, a p-side electrode 225, and a protective layer227.

The substrate 201 is e.g. a silicon substrate. The substrate 201 has anupper surface US and a lower surface BS opposed to each other.

The n-side electrode 203 is provided on the lower surface BS of thesubstrate 201. The n-side electrode 203 contains e.g. metal such asgold, nickel, titanium, and aluminum.

The metal layer 205 is provided on the upper surface US of the substrate201. The central part of the upper surface of the metal layer 205protrudes toward the Z-direction. The metal layer 205 contains e.g. tin.

The barrier layer 207 is provided on the metal layer 205 along the uppersurface of the metal layer 205. The central part of the upper surface ofthe barrier layer 207 protrudes toward the Z-direction like the metallayer 205. The barrier layer 207 has a structure in which e.g. atitanium layer and a platinum layer are stacked.

The n-side contact layer 209 is provided on part of the barrier layer207. The protrusion 209 c of the upper surface of the n-side contactlayer 209 protrudes toward the Z-direction like the barrier layer 207.The n-side contact layer 209 is e.g. an aluminum layer.

The insulating layer 211 is provided on part of the barrier layer 207and part of the n-side contact layer 209. The protrusion 209 c of then-side contact layer 209 is surrounded with the insulating layer 211along the X-Y plane. However, the upper surface of the protrusion 209 cis not covered with the insulating layer 211. The insulating layer 211contains an insulating material such as silicon oxide or siliconnitride.

The barrier layer 213 is provided on the insulating layer 211. Thebarrier layer 213 is shaped like a ring and provided around theprotrusion 209 c along the X-Y plane. The barrier layer 213 has astructure in which e.g. a titanium layer and a gold layer are stacked.

The p-side contact layer 215 is provided on the barrier layer 213. Thep-side contact layer 215 is e.g. a silver layer.

The p-type semiconductor layer 217 is provided on the barrier layer 213and the p-side contact layer 215. The p-type semiconductor layer 217 isin ohmic contact with the p-side contact layer 215. The p-typesemiconductor layer 217 is made of e.g. gallium nitride containingp-type impurity.

The light emitting layer 218 is provided on the p-type semiconductorlayer 217. The light emitting layer 218 is e.g. an undoped galliumnitride layer. The p-side contact layer 215, the p-type semiconductorlayer 217, and the light emitting layer 218 are provided like a ringaround the protrusion 209 c like the barrier layer 213.

The spacer 221 is provided on part of the protrusion 209 c. The spacer221 contains e.g. silicon oxide or silicon nitride.

The n-type semiconductor layer 219 is provided on the light emittinglayer 218, the protrusion 209 c, and the spacer 221. The n-typesemiconductor layer 219 is in ohmic contact with the n-side contactlayer 209. The n-type semiconductor layer 219 is e.g. a gallium nitridelayer containing n-type impurity.

Each side surface of the p-type semiconductor layer 217, the lightemitting layer 218, and the n-type semiconductor layer 219 is coveredwith the protective layer 227. The protective layer 227 contains e.g.silicon nitride.

The p-side electrode 225 is provided on the barrier layer 213 and spacedfrom the p-type semiconductor layer 217. The p-side electrode 225 iselectrically connected to the p-side contact layer 215 via the barrierlayer 213. The p-side electrode 225 contains metal such as gold, nickel,titanium, and aluminum.

FIG. 18 is an enlarged sectional view showing part of the upper surfaceof the semiconductor light emitting device 2 according to the secondembodiment.

More specifically, FIG. 18 shows the structure of a portion of the uppersurface of the n-type semiconductor layer 219 which is not covered withthe protective layer 227 and from which light is extracted outside.

As shown in FIG. 18, a plurality of protrusions 119 are provided on theupper surface of the n-type semiconductor layer 219 as in thesemiconductor light emitting device 1. The protrusion 119 has a firstportion 119 a and a second portion 119 b. The side surface S1 and theside surface S2 are inclined with respect to the Z-direction. The sidesurface S2 is curved so as to be convex downward.

Also in this embodiment, as in the first embodiment, a plurality ofprotrusions 119 are provided on the upper surface of the stacked bodyLB. Thus, the surface area of the upper surface of the stacked body LBcan be increased. This can improve the efficiency of light extractionfrom the semiconductor light emitting device.

As in the variations of the first embodiment, a plurality of protrusions119 and a plurality of protrusions 121 may be provided on the uppersurface of the stacked body LB.

Here, the semiconductor light emitting device has been described withreference to an example in which an n-side electrode is provided on thelower surface of the substrate 201 and a p-side electrode 225 isprovided on the lateral side of the stacked body LB. However, theinvention according to this embodiment is also applicable to thesemiconductor light emitting device in which the positional relationshipof the n-side electrode and the p-side electrode is reversed.

(First Variation)

FIG. 19 is a sectional view of a semiconductor light emitting device 2 aaccording to a first variation of the second embodiment.

FIG. 20 is an enlarged sectional view showing part of the upper surfaceof the semiconductor light emitting device 2 a according to the firstvariation of the second embodiment.

As shown in FIG. 19, in the semiconductor light emitting device 2 a, anundoped semiconductor layer 220 is provided on the n-type semiconductorlayer 219. The semiconductor layer 220 is e.g. an undoped galliumnitride layer. The stacked body LB includes the p-type semiconductorlayer 217, the light emitting layer 218, the n-type semiconductor layer219, and the semiconductor layer 220.

As shown in FIG. 20, a plurality of protrusions 119 are provided on theupper surface of the semiconductor layer 220 as in the semiconductorlight emitting device 2.

The light absorption coefficient in the undoped semiconductor layer issmaller than the light absorption coefficient in the impurity-dopedsemiconductor layer. In the semiconductor light emitting deviceaccording to this variation, an undoped semiconductor layer 220 isprovided on the n-type semiconductor layer 219. Light is extractedoutside from the upper surface of the semiconductor layer 220. Thus,this variation can improve the external light extraction efficiencycompared with the semiconductor light emitting device 2.

(Second Variation)

FIG. 21 is a sectional view of a semiconductor light emitting device 2 baccording to a second variation of the second embodiment.

FIG. 22 is a partially enlarged plan view of the stacked body LB of thesemiconductor light emitting device 2 b according to the secondvariation of the second embodiment.

FIG. 23 is a sectional view taken along A-A′ in FIG. 22.

The protective layer 227 is omitted in FIG. 22.

In the semiconductor light emitting device 2 b, a plurality of recessesR are formed in the upper surface of the stacked body LB including thep-type semiconductor layer 217, the light emitting layer 218, and then-type semiconductor layer 219. Preferably, as shown in FIG. 21, therecess R is formed on the region other than the protrusion 209 c toprevent etching of the protrusion 209 c of the n-side contact layer 209.Part of the p-type semiconductor layer 217 and part of the lightemitting layer 218 are exposed outside the stacked body LB through therecess R. A protective layer 227 is provided along the upper surface ofthe stacked body LB to prevent external exposure of the light emittinglayer 218. Part of the protective layer 227 is provided inside therecess R in the upper surface of the stacked body LB.

As shown in FIG. 22, the recesses R are provided in a plurality in theupper surface of the stacked body LB along the X-Y plane. As an example,six recesses R are arranged around one recess R.

As shown in FIG. 23, the width of the recess R is narrowed downward. Therecess R has a side surface S5 and a side surface S6 inclined withrespect to the Z-direction. The side surface S5 is curved so as to beconvex upward. The side surface S6 is located below the side surface S5.

In the example shown in FIG. 23, the side surface of the light emittinglayer 118 is included in the side surface S5. However, the side surfaceof the light emitting layer 118 may be included in the side surface S6.

The light emitted from the light emitting layer 118 is injected from thestacked body LB into the protective layer 227 and extracted outside fromthe upper surface of the protective layer 227. The side surface S5 ofthe recess R is curved so as to be convex upward. Thus, the surface areaof the upper surface of the stacked body LB can be made larger than inthe case where the side surface of the recess R is uniformly inclined.That is, this variation can improve the efficiency of light extractionfrom the stacked body LB to the protective layer 227. Thus, theefficiency of light extraction from the semiconductor light emittingdevice can be improved.

Part of the side surface of the recess R is curved so as to be convexupward. In this case, the side surface S5 located above is curved. Thiscan reduce the possibility that the light injected from the side surfaceof the recess R into the protective layer 227 is incident into thestacked body LB through the side surface of the recess R compared withthe case where the side surface S6 is curved.

The recess R having the side surface S5 is provided in the upper surfaceof the stacked body LB. Thus, when the surface area of the upper surfaceof the stacked body LB is increased, the region of the n-typesemiconductor layer 119 having a thick film thickness can be made largerthan in the case where a protrusion is formed on the upper surface ofthe stacked body LB. This can reduce the electrical resistance in then-type semiconductor layer 119 and reduce the power consumption of thesemiconductor light emitting device. Alternatively, by the amount ofreducing the electrical resistance in the n-type semiconductor layer119, the film thickness of the n-type semiconductor layer 119 can bethinned, and the semiconductor light emitting device can be downsized.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

REFERENCE SIGNS LIST

-   1, 1 a-1 e, 2, 2 a, 2 b semiconductor light emitting device-   109 p-type semiconductor layer-   111 light emitting layer-   113 n-type semiconductor layer-   119, 121 protrusion-   123 semiconductor layer-   217 p-type semiconductor layer-   218 light emitting layer-   219 n-type semiconductor layer-   220 semiconductor layer-   LB stacked body-   R recess

1-13. (canceled) 14: A semiconductor light emitting device comprising: a stacked body including a first semiconductor layer of a first conductivity type, a light emitting layer provided on the first semiconductor layer, and a second semiconductor layer of a second conductivity type provided on the light emitting layer, the stacked body including a first protrusion and a second protrusion on an upper surface of the stacked body, the first protrusion and the second protrusion protruding in a first direction from the first semiconductor layer to the light emitting layer, lengths of the first protrusion and the second protrusion in a second direction perpendicular to the first direction decreasing toward the first direction, and the first protrusion including: a first portion having a first side surface inclined with respect to the first direction; and a second portion provided below the first portion and having a second side surface inclined with respect to the first direction, the second side surface being curved so as to be convex downward, the second protrusion including: a third portion having a third side surface inclined with respect to the first direction; and a fourth portion provided below the third portion and having a fourth side surface inclined with respect to the first direction, the fourth side surface being curved so as to be convex downward, length of the first protrusion in the first direction being longer than length of the second protrusion in the first direction. 15: The device according to claim 14, wherein length in the first direction of the second portion is longer than length in the first direction of the first portion. 16: The device according to claim 14, wherein inclination of at least part of the second side surface with respect to the first direction is smaller than inclination of the first side surface with respect to the first direction. 17: The device according to claim 14, wherein length in the first direction of the first portion is longer than length in the first direction of the third portion. 18: The device according to claim 14, wherein inclination of at least part of the fourth side surface with respect to the first direction is smaller than inclination of the third side surface with respect to the first direction, and length in a second direction perpendicular to the first direction of the first protrusion at a first position in the first direction is longer than length in the second direction of the second protrusion at the first position. 19: The device according to claim 18, wherein length in the first direction of the first portion is longer than length in the first direction of the third portion. 20: The device according to claim 14, wherein the stacked body further includes an undoped third semiconductor layer provided on the second semiconductor layer, and the first protrusion is formed on an upper surface of the third semiconductor layer. 21: The device according to claim 14, wherein the stacked body further includes an undoped third semiconductor layer provided on the second semiconductor layer, and at least part of the first portion is at least part of the third semiconductor layer. 22: The device according to claim 14, wherein at least part of the second portion is at least part of the first semiconductor layer. 23: The device according to claim 14, wherein the first side surface is curved so as to be convex upward. 24: A semiconductor light emitting device comprising: a stacked body including a first semiconductor layer of a first conductivity type, a light emitting layer provided on the first semiconductor layer, and a second semiconductor layer of a second conductivity type provided on the light emitting layer, a first recess being provided in an upper surface of the stacked body, dimension of the first recess in a second direction perpendicular to a third direction from the light emitting layer to the first semiconductor layer decreasing toward the third direction, the light emitting layer being exposed through the first recess, and the first recess having: a first side surface inclined with respect to the first direction and curved so as to be convex upward; and a second side surface located below the first side surface and inclined with respect to the first direction. 